In the operation of gas pipelines water and hydrocarbon vapors tend to condense especially during pressure changes across the valves, orifice fittings, pumps, etc. thereby causing the build-up of liquid deposits in the pipeline. These liquid deposits tend to become entrapped in low places in the pipeline and otherwise reduce the cross-section of dimension of the pipeline passages so that unless regularly cleaned of such deposits, the production capacity of the pipeline will be reduced.
Large transportation lines for natural gas are frequently cleaned of condensate, sediment and other debris that might be present in the gas, such cleaning being accomplished by various types of cleaning devices, typically referred to as "pigs" which are passed through the pipeline along with the flowing gas. Various types of pigs such as spheres, line scrapers, bullets, cup pigs, etc. are forced through the pipelines at frequent intervals for the purpose of forcing liquid matter through the pipeline along with the flowing gaseous medium. In some cases, high pressure pipelines transporting fluid material are required to carry a liquid phase simultaneously with the gaseous phase. Such liquids may be present in the gas when it is injected into the pipeline as in full well stream transport or liquids such as drip gasoline or crude oil may be injected into a flowing gas stream to be transported along with the gas.
Where liquid constituents are present in a gas pipeline especially where several different liquids may be transported along with the flowing gas, it will be appropriate to utilize pigs, such as cup pigs, for the purpose of separating the liquids. Accordingly, it is desirable to provide a pig launching mechanism having the capability of sequentially launching a plurality of pigs such as cup pigs into a continuously flowing gas pipeline so that the pipeline will remain clear of any accumulations of sediment, condensate, and so that liquid constituents being transported by the pipelines can remain separated.